After few years of evolution, patients with Parkinson's disease may develop apathy, with different degrees of severity. Apathy is characterized by a loss of interest for the others and for activities. The lack of social interactions in these patients may be due to an impairment in decoding emotional facial expression. Indeed, facial expression recognition, which is necessary to understand other's emotional state, requires a subclinical facial mimicking of the expression observed. Yet, one of the clinical signs of PD is amimia.